Geochemical petroleum exploration method



United statement 7 3,428,431 GEOCHEMICAL PETROLEUM EXPLORATION METHODGale K. Billings, Tulsa, Okla., assignor, by mesne assignments, toSinclair Research, Inc., New York, N.Y., a

corporation of Delaware No Drawing. Filed May 12, 1965, Ser. No. 455,330U.S. Cl. 23230 1 Claim Int. Cl. 601v 9/00, 33/18; G01n 33/24 ABSTRACT OFTHE DISCLOSURE The method of exploration for petroleum deposits whichcomprises collecting samples of formation waters from wells anddetermining the concentration of at least one transition metal in saidwaters as a component indicative of the presence of petroleum deposits.

This invention relates to a method of geochemical prospecting for hiddenhydrocarbon deposits by analyzing subsurface brines or other waters forthe presence of dissolved transition metals, in particular metals of thefirst transition series such as iron, cobalt, manganese, etc.

The search for hydrocarbon deposits by geochemistry has heretofore beenconducted by seeking actual evidence of leakage from the depositsthemselves. One method of geochemical prospecting has been conducted bymaking systematic collection of soil samples over an area to be mappedand testing the soil samples for a variety of components believedindicative of the presence of hydrocarbon deposits. Inorganic substancesconsidered indicative include carbonates, bicanbonates, sulfates,sulfides, halides, etc. Among the other components for which thesesamples have been tested are the lighter paraflinic hydrocarbons whichare presumed to have migrated from deep subsurface hydrocarbon deposits.One of the difiiculties en countered with this method of prospecting isthat generally there is a wide variation of the sorpti ve and retentivecapacities of the soil samples taken over a plurality of locations. Thisis due primarily to the differences in chemical and physical propertiesof the soil itself. A pattern of such concentration values may thus notgive a true indication of the proximity of hydrocarbon deposits. Inother known methods of geochemical prospecting, techniques have beenused for detecting extremely small concentrations of crude hydrocarbonsdispersed in drilling fluids. One of the problems which has beenencountered in this type of prospecting for crude oil deposits is thatpositive indications are obtained when the drilling fluid iscontaminated with refined petroleum products, such as pipe-thread greaseor lubricating oils. The present invention is directed to overcoming theproblems encountered in geochemical prospecting such as discussed above.

In general, the present invention is directed to a method of geochemicalprospecting'wherein information concerning the proximity of hydrocarbondeposits or source beds is derived by gll ecting aqueoussubterraneansamples from prospect areas and wildcatwells and determining theconcentration of dissolved transition metalsinthe samples. The presenceof these dissolved transition metals is an indication that thesesubterranean waters have been in contact with or are near apetroliferous deposit since the reaction between crude oil and itsassociatedformation waters results in reduction of the oxidizingcapability of the waters. In other words, the waters are n g lgng c rcapable of oxidizing the transition metals sugh asiign, nickel, EobalLietci, and the 'trahsitio'n metals are, therefore, reduced. Thisreduction leads to an increase in the concentration of the transitionmetals in the formation waters because the metals are soluble in thereduced state but are highly insoluble in the oxidized state. Thus, theproximity to petroleum deposits is indicated by an increase in theconcentration of transition metals in the X n formation waters. Bymeasuring the concentration of di sso l ved transition 7 metals in fluidsamples obtained for instance froth wild 4-" cat'wells, even though'considered to be dry holes, it is possible to determine whether aparticular formation is completely barren or whether nearby portions maybe petroliferous. Such information obtained by dt ct ing fse -iu th -sun eseuatersncbtinesjro wilggytygells. may guide further drillingactivity in the area. Transition metals in varying concentrations havebeen found in tests on dry holes and increasing metal concentration isinterpreted as indicating the direction toward petroleum deposits.

In practicing this invention any suitable rnejhod of t analysis-may beemployed, for example, atomic a-bsorpt i 9 n. The samples for analysismay comprise formation t waters obtained by swabbing, drill-stem testfluids obtained from a drill-stem test, or samples of underground watersobtained by any convenient means.

Generally speaking, in accordance with this invention, formation watersamples are analyzed for their water soluble transition metals content,after which th e results of such analyses are plotted. The results, whenplotted, either in plan or in profile, or both, will show a pattern ofgenerally increasing concentration toward an oil or gas def posit. Itis, of course, true that there will be variations i" in theconcentrations of the transition metals in the formation waters fromdifferent localities due to the history of the waters, formationsurrounding the waters, etc., even in the absence of petroleum deposits;however, larger variations will be found due to the presence ofburiedpetroleum deposits and, as a rule, the small natural variationsare negligible as compared to the larger variations resulting from thepresence of buried petroleum deposits.7 .f"\ In the present invention,it is a trend, i.e. increase in the 6 amount of transition metals in thewater, and not the amount per se, that is indicative of the presence ofpetroleum. Also, although in some areas it :has been found upon analysisthat certain transition metals may not yield distinctive patterns,usually this failure to give a pattern adjacent a producing area will beconfined to one, or a few, metals and the characteristic pattern will beshown by analysis for any number of the other transition metals condemnan a'realbeca se analysis for one metal failed to I give a characteristipattern, and the patterns of other metals should be obtained so that itcan be determined whether or not a significant pattern is obtained witha majority of the metals. Even if a significant pattern is obtained withonly one metal, which would indeed be a rare case, further explorationof the area would be in order.

Table 1 lists the concentrations of some transition metals in variousformation waters, e.g., formation brines, from oil producing areas.These data compared with sea water demonstrate that the concentrationsin formation waters are often hundreds of times that of sea water.

TABLE 1 P.p.m. Fo P.p.m. Co P.p.m. Mn

The transition metal concentrations illustrated above reveal the generalnature of the results attainable by the practice of the presentinvention. It is to be understood that the present invention is notlimited to the particular metals listed but encompasses those metals,e.g. transition metals, which are soluble in the reduced state but areinsoluble in the oxidized state, especially the metals of the firsttransition series including in addition to iron, cobalt and manganese,nickel, vanadium, titanium, chromium, and scandium.

It is claimed:

1. The method of exploration for petroleum deposits which comprisessystematically collecting formation water gt nples from a prospect areaam concentration in the original samples of at least two a l in thereduced state and insoluble in the oxidized state as an indication ofthe proximity of petroleum deposits,

UNITED STATES PATENTS 2/ 1943 Horvitz 23-230 OTHER REFERENCES Graham B.Moody, Petroleum Exploration Handbook, Chapt. 5, p. 11 and Chapt. 22, p.14, McGraw- Hill Book Co., Inc., New York, 1961.

MORRIS O. WOLK, Primaly Examiner.

S. MARANTZ, Assistant Examiner.

U.S. C1. X.R.

